Kwonseop Kim

Wnt-7a Causes Loss of Differentiated Phenotype and Inhibits Apoptosis of Articular Chondrocytes via Different Mechanisms

Although regulation of chondrogenesis and cartilage development by Wnt signaling is well established, the function of Wnt in the maintenance and destruction of cartilage remains largely unknown. Here we investigated the involvement and regulatory mechanisms of Wnt signaling in cartilage destruction. We found that interleukin-1β, the primary pro-inflammatory cytokine involved in cartilage destruction, induces expression of Wnt-5a and -7a in primary culture articular chondrocytes. The level of β-catenin was also increased in chondrocytes of arthritic cartilage, suggesting the association of Wnt/β-catenin signaling with arthritic cartilage destruction. In addition, our results show that Wnt-7a induces dedifferentiation and inhibits NO-induced apoptosis of primary culture articular chondrocytes. Wnt-7a induces dedifferentiation of articular chondrocytes by stimulating transcriptional activity of β-catenin, whereas NO-induced apoptosis is inhibited via the activation of cell survival signaling, such as phosphatidylinositol 3-kinase and Akt, which block apoptotic signaling cascade. Our results collectively suggest that Wnt-7a is associated with cartilage destruction by regulating the maintenance of differentiation status and the apoptosis of articular chondrocytes via different mechanisms.

Regulation of Notch1/NICD and Hes1 expressions by GSK-3α/β

Notch signaling is controlled at multiple levels. In particular, stabilized Notch receptor activation directly affects the transcriptional activations of Notch target genes. Although some progress has been made in terms of defining the regulatory mechanism that alters Notch stability, it has not been determined whether Notch1/NICD stability is regulated by GSK-3α. Here, we show that Notch1/NICD levels are significantly regulated by GSK-3β and by GSK-3α. Treatment with LiCl (a specific GSK-3 inhibitor) or the overexpression of the kinase-inactive forms of GSK-3α/β significantly increased Notch1/NICD levels. Endogenous NICD levels were also increased by either GSK-3α/β- or GSK-3α-specific siRNA. Furthermore, it was found that GSK-3α binds to Notch1. Deletion analysis showed that at least three Thr residues in Notch1 (Thr-1851, 2123, and 2125) are critical for its response to LiCl, which increased not only the transcriptional activity of endogenous NICD but also Hes1 mRNA levels. Taken together, our results indicate that GSK-3α is a negative regulator of Notch1/NICD.

δ-Catenin Induced Dendritic Morphogenesis: An Essential Role of p190RhoGEF Interaction through Akt1 Mediated Phosphorylation

δ-Catenin was first identified through its interaction with Presenilin-1 and has been implicated in the regulation of dendrogenesis and cognitive function. However, the molecular mechanisms by which δ-catenin promotes dendritic morphogenesis were unclear. In this study, we demonstrated δ-catenin interaction with p190RhoGEF, and the importance of Akt1-mediated phosphorylation at Thr-454 residue of δ-catenin in this interaction. We have also found that δ-catenin overexpression decreased the binding between p190RhoGEF and RhoA, and significantly lowered the levels of GTP-RhoA but not those of GTP-Rac1 and -Cdc42. δ-Catenin T454A, a defective form in p190RhoGEF binding, did not decrease the binding between p190RhoGEF and RhoA. δ-Catenin T454A also did not lower GTP-RhoA levels and failed to induce dendrite-like process formation in NIH 3T3 fibroblasts. Furthermore, δ-catenin T454A significantly reduced the length and number of mature mushroom shaped spines in primary hippocampal neurons. These results highlight signaling events in the regulation of δ-catenin-induced dendrogenesis and spine morphogenesis.

Beta-catenin modulates the level and transcriptional activity of Notch1/NICD through its direct interaction

Wnt and Notch1 signaling pathways play an important role in a variety of biological processes including embryonic induction, the polarity of cell division, cell fate, and cell growth. Although there is evidence that the two main signaling pathways can modulate each other, the precise mechanism is not completely understood. This report shows that beta-catenin can regulate the level and transcriptional activity of the Notch1 and Notch1 intracellular domain (NICD). The in vivo and in vitro results demonstrate that beta-catenin binds with Notch1 and NICD, for which its Armadillo repeat domain is essential. It was further demonstrated that beta-catenin could upregulate the level of Notch1 and NICD, possibly by competing the common ubiquitin-dependent degradation machinery. In addition, beta-catenin enhanced the transcriptional activity of NICD on the hairy and enhancer of split 1 (HES1) and CSL through its C-terminal transactivation domain. This effect of cooperative regulation by beta-catenin could also be observed in bone morphogenetic protein 2 (BMP2) induced osteogenic differentiation of C2C12 cells. beta-catenin coexpression with NICD enhanced the alkaline phosphatase (ALP) activity in C2C12 cells compared with either beta-catenin or NICD expression alone. Culturing C2C12 cells on Delta-1 coated dishes together with Wnt3-conditioned media induced noticeable increases in ALP staining, verifying that employed physiological levels of NICD and beta-catenin are sufficient to induce ALP activation. Furthermore, effects of beta-catenin on Notch1 were dramatically diminished by overexpressed LEF1. Overall, our data suggest that beta-catenin can act as a switching molecule between the classical TCF/LEF1 mediated pathway and NICD mediated pathway.

Dyrk1A‐mediated phosphorylation of Presenilin 1: a functional link between Down syndrome and Alzheimer’s disease

J. Neurochem. (2010) 115, 574–584.

WNK4 phosphorylates ser206 of claudin‐7 and promotes paracellular Cl− permeability

Mutations in WNK4 have been linked to hypertension in PHAII. Paracellular ion transport has been reported to be involved in this disease process; however, the specific molecular target has not been identified. In this study, we found that TJ protein claudin‐7 and WNK4 were partially co‐localized in renal tubules of rat kidney and co‐immunoprecipitated in kidney epithelial cells. The wild‐type and PHAII‐causing mutant, but not the kinase‐dead mutant, phosphorylated claudin‐7. We have identified ser206 in the COOH‐terminus of claudin‐7 as a putative phosphorylation site for WNK4. More importantly, disease‐causing mutant enhanced claudin‐7 phosphorylation and significantly increased paracellular permeability to Cl−.

GSK-3 Phosphorylates δ-Catenin and Negatively Regulates Its Stability via Ubiquitination/Proteosome-mediated Proteolysis

δ-Catenin was first identified because of its interaction with presenilin-1, and its aberrant expression has been reported in various human tumors and in patients with Cri-du-Chat syndrome, a form of mental retardation. However, the mechanism whereby δ-catenin is regulated in cells has not been fully elucidated. We investigated the possibility that glycogen-synthase kinase-3 (GSK-3) phosphorylates δ-catenin and thus affects its stability. Initially, we found that the level of δ-catenin was greater and the half-life of δ-catenin was longer in GSK-3β−/− fibroblasts than those in GSK-3β+/+ fibroblasts. Furthermore, four different approaches designed to specifically inhibit GSK-3 activity, i.e. GSK-3-specific chemical inhibitors, Wnt-3a conditioned media, small interfering RNAs, and GSK-3α and -3β kinase dead constructs, consistently showed that the levels of endogenous δ-catenin in CWR22Rv-1 prostate carcinoma cells and primary cortical neurons were increased by inhibiting GSK-3 activity. In addition, it was found that both GSK-3α and -3β interact with and phosphorylate δ-catenin. The phosphorylation of ΔC207-δ-catenin (lacking 207 C-terminal residues) and T1078A δ-catenin by GSK-3 was noticeably reduced compared with that of wild type δ-catenin, and the data from liquid chromatography-tandem mass spectrometry analyses suggest that the Thr1078 residue of δ-catenin is one of the GSK-3 phosphorylation sites. Treatment with MG132 or ALLN, specific inhibitors of proteosome-dependent proteolysis, increased δ-catenin levels and caused an accumulation of ubiquitinated δ-catenin. It was also found that GSK-3 triggers the ubiquitination of δ-catenin. These results suggest that GSK-3 interacts with and phosphorylates δ-catenin and thereby negatively affects its stability by enabling its ubiquitination/proteosome-mediated proteolysis.

δ-Catenin promotes prostate cancer cell growth and progression by altering cell cycle and survival gene profiles

Backgroundδ-Catenin is a unique member of β-catenin/armadillo domain superfamily proteins and its primary expression is restricted to the brain. However, δ-catenin is upregulated in human prostatic adenocarcinomas, although the effects of δ-catenin overexpression in prostate cancer are unclear. We hypothesized that δ-catenin plays a direct role in prostate cancer progression by altering gene profiles of cell cycle regulation and cell survival.ResultsWe employed gene transfection and small interfering RNA to demonstrate that increased δ-catenin expression promoted, whereas its knockdown suppressed prostate cancer cell viability. δ-Catenin promoted prostate cancer cell colony formation in soft agar as well as tumor xenograft growth in nude mice. Deletion of either the amino-terminal or carboxyl-terminal sequences outside the armadillo domains abolished the tumor promoting effects of δ-catenin. Quantitative RT2 Profiler™ PCR Arrays demonstrated gene alterations involved in cell cycle and survival regulation. δ-Catenin overexpression upregulated cyclin D1 and cdc34, increased phosphorylated histone-H3, and promoted the entry of mitosis. In addition, δ-catenin overexpression resulted in increased expression of cell survival genes Bcl-2 and survivin while reducing the cell cycle inhibitor p21Cip1.ConclusionTaken together, our studies suggest that at least one consequence of an increased expression of δ-catenin in human prostate cancer is the alteration of cell cycle and survival gene profiles, thereby promoting tumor progression.

δ-Catenin promotes E-cadherin processing and activates β-catenin-mediated signaling: implications on human prostate cancer progression.

δ-Catenin binds the juxtamembrane domain of E-cadherin and is known to be overexpressed in some human tumors. However, the functions of δ-catenin in epithelial cells and carcinomas remain elusive. We found that prostate cancer cells overexpressing δ-catenin show an increase in multi-layer growth in culture. In these cells, δ-catenin colocalizes with E-cadherin at the plasma membrane, and the E-cadherin processing is noticeably elevated. E-Cadherin processing induced by δ-catenin is serum-dependent and requires MMP- and PS-1/γ-secretase-mediated activities. A deletion mutant of δ-catenin that deprives the ability of δ-catenin to bind E-cadherin or to recruit PS-1 to E-cadherin totally abolishes the δ-catenin-induced E-cadherin processing and the multi-layer growth of the cells. In addition, prostate cancer cells overexpressing δ-catenin display an elevated total β-catenin level and increase its nuclear distribution, resulting in the activation of β-catenin/LEF-1-mediated transcription and their downstream target genes as well as androgen receptor-mediated transcription. Indeed, human prostate tumor xenograft in nude mice, which is derived from cells overexpressing δ-catenin, shows increased β-catenin nuclear localization and more rapid growth rates. Moreover, the metastatic xenograft tumor weights positively correlate with the level of 29kD E-cadherin fragment, and primary human prostate tumor tissues also show elevated levels of δ-catenin expression and the E-cadherin processing. Taken together, these results suggest that δ-catenin plays an important role in prostate cancer progression through inducing E-cadherin processing and thereby activating β-catenin-mediated oncogenic signals.

Identification of E2F1 as a positive transcriptional regulator for delta-catenin

delta-Catenin is upregulated in human carcinomas. However, little is known about the potential transcriptional factors that regulate delta-catenin expression in cancer. Using a human delta-catenin reporter system, we have screened several nuclear signaling modulators to test whether they can affect delta-catenin transcription. Among beta-catenin/LEF-1, Notch1, and E2F1, E2F1 dramatically increased delta-catenin-luciferase activities while beta-catenin/LEF-1 induced only a marginal increase. Rb suppressed the upregulation of delta-catenin-luciferase activities induced by E2F1 but did not interact with delta-catenin. RT-PCR and Western blot analyses in 4 different prostate cancer cell lines revealed that regulation of delta-catenin expression is controlled mainly at the transcriptional level. Interestingly, the effects of E2F1 on delta-catenin expression were observed only in human cancer cells expressing abundant endogenous delta-catenin. These studies identify E2F1 as a positive transcriptional regulator for delta-catenin, but further suggest the presence of strong negative regulator(s) for delta-catenin in prostate cancer cells with minimal endogenous delta-catenin expression.